This invention relates to an engine control method and engine control structure for a vehicle and more particularly to an improved engine control that prevents unwanted transmission action such as clutch chatter.
In small vehicles such as scooters, engine revolution is often transmitted to the driven wheel through an automatic transmission. Vehicles with belt type continuously variable transmissions have been widely in use. In such cases, the transmission system is typically provided with a starting centrifugal friction clutch. The centrifugal friction clutch becomes engaged through centrifugal force when the rotational speed rises close to a predetermined value and the friction force increases as the rotational speed rises. This enables a smooth start of the vehicle.
However, in the friction clutch, a chattering phenomenon caused by vibrations or oscillation may happen during the engagement of the clutch. If this phenomenon happens, not only may the clutch and the transmission system be damaged, but the rider and passengers may experience an uncomfortable feeling. To avoid or minimize these effects the size and material of the clutch have been improved at some cost disadvantage.
As a further or substitute remedy, the engine power is reduced by a given amount in a predetermined speed range near the engine speed at which the clutch is connected. One way this has been done is to retard ignition timing to lower engine output so that vibrations are restricted during clutch connection. Alternatively this may be done by skipping or misfiring of the spark plug. In such methods, the delayed angle or skipping is set to a fixed value.
However, the juddering phenomenon doesn't always occur. The occurrence depends on running conditions such as load on the vehicle; wear conditions of the friction members of the clutch, or other factors. In such cases, there is no need of reducing engine power, but the previous systems do so a predetermined speed range at all times. Therefore not only is engine combustion impaired with decreased fuel efficiency, but also undesirable exhaust emissions are increased.
Thus, it is a principle object of this invention to provide an improved engine control method and system for a vehicle capable of preventing the generation of transmission vibrations particularly caused by connection and disconnection of a clutch.